Integral Self-Contained Drillstring Compensator

ABSTRACT

An integral self-contained drillstring compensator includes at least one high pressure air cylinder, an accumulator, and a compensating cylinder, which are fluidly coupled to one another. The high pressure air cylinders include a compressible gas that is communicable to the accumulator, which has fluid included therein. The compressible gas provides a pressure on the fluid, thereby allowing the fluid to communicable between the accumulator and the compensating cylinder. The fluid causes a cylinder rod within the compensating cylinder to extend and retract from the compensating cylinder, thereby providing compensation during heaves. The drillstring compensator optionally includes a low pressure air cylinder to store a low pressure compressible fluid that communicates with the compensating cylinder.

CROSS REFERENCE TO RELATED APPLICATIONS

This patent application claims priority under 35 U.S.C. §119(e) to U.S. Provisional Patent Application No. 62/141,067 titled “Integral Self-Contained Drillstring Compensator” filed on Mar. 31, 2015, the entire content of which is hereby incorporated by reference herein.

TECHNICAL FIELD

The present disclosure relates to an inline self-contained compensator apparatus and method for use and installation on floating drilling rigs and workover or production vessels. In particular, the present disclosure relates to an inline self-contained compensator apparatus that functions as a back-up system for the primary or main heave compensation system of a floating drilling rig or vessel in the event the primary heave compensation system becomes disabled or inoperative.

BACKGROUND OF THE INVENTION

Drilling for oil and gas off-shore is completed from one of two types of drilling rigs: rigs that are supported by the sea floor (such as fixed drilling rigs or jack-up drilling rigs) or rigs that float on the surface of the water (such as drill ships or semi-submersible drilling rigs). Although drilling operations conducted from these two types of drilling rigs are similar, at least one major difference exists: drill ships or semi-submersible drilling rigs move with the waves of the sea, while fixed or jack-up drilling rigs remain fixed to the sea floor.

The movement of drill ships or semi-submersible drilling rigs with the waves of the sea presents a unique problem in drilling with these types of rigs. First, in any drilling operation conducted from floating rigs, compensation for the rig's tendency to heave, that is move up and down with the waves, must be accounted for. In particular, as the floating rig moves up and down, the drill string and drill bit extending below the rig will also move up and down. For a drill bit to perform as efficiently as possible, the desired or optimum weight on the drill bit, i.e., the downward force applied to the bit, must be kept as constant as possible. Heave, however, removes weight from the drill bit as the ship or rig rides to the crest of a wave, and puts weight back on the drill bit as the ship or rig rides down into the trough between waves. This fluctuation in the force applied on the drill bit severely hinders an operator's ability to drill the well bore. Although heave presents a problem in drilling with these types of rigs, heave presents similar problems with other drilling activities, such as well completions, well testing, well interventions, well production, and other operations.

Perhaps more importantly, heave creates the potential for blowouts due to a potential fracturing or breaking of the production tubing during testing, workover, or completion operations. Specifically, once the well bore has been drilled, the oil and gas reserves are brought up to the floating rig through production tubing that runs from the rig to the producing zones of the well bore, typically thousands of feet below the sea floor. The string of production tubing consists of dozens, if not hundreds, of joints of tubing connected together. The production tubing is supported by and is kept in tension by the drill hook and drawworks on the drilling rig to keep the string from buckling.

The production tubing is typically held in place within the well bore by one or more production packers. Because the production tubing is held in place within the well bore, any rise of the floating drilling rig due to heave will increase the tension on the production tubing string and could cause the string to fracture or break. A fracturing or breaking of the production tubing string would allow the oil or gas within the tubing to leak, creating the potential for a blowout.

To account for the problems associated with heave, floating drilling rigs are equipped with a heave compensation system. The heave compensation system is typically in the form of an active heave drawworks system or a system that is an integral part of the drilling derrick or mounted directly on an extension of the traveling block. When functioning properly, these primary heave compensation systems are capable of protecting against the effects of heave. However, many prior art floating drilling rigs are generally not equipped with a back-up, or secondary, heave compensation system that operates in the event the primary heave compensation system is not functioning properly or becomes inoperative. In such a situation, the floating drilling rig will have no way to compensate for heave. Some prior art floating drilling rigs are equipped with a back-up, or secondary, heave compensation system that operates in the event the primary heave compensation system fails, but these systems are very large and require much floor space on the rigs for air compression systems and hoses extending from the air compression systems to the secondary heave compensation system.

Since drill ships or semi-submersible drilling rigs have limited space available on the derrick, what is needed is a heave compensation system that acts as a back-up system to the primary heave compensation system and that is compact and self-contained such that the limited space available on a floating drilling rig is affected in a lesser manner.

BRIEF DESCRIPTION OF THE DRAWINGS

The foregoing and other features and aspects of the invention are best understood with reference to the following description of certain exemplary embodiments, when read in conjunction with the accompanying drawings, wherein:

FIG. 1 is a partial schematic representation of a derrick and drill floor of a floating vessel showing an integral self-contained drillstring compensator and the various positions of the integral self-contained drillstring compensator during installation in accordance with an exemplary embodiment;

FIG. 2 is a partial perspective view of the integral self-contained drillstring compensator of FIG. 1 in accordance with an exemplary embodiment;

FIGS. 3A-3D are several views of the integral self-contained drillstring compensator of FIG. 2 in accordance with an exemplary embodiment;

FIG. 4 is a cross-sectional schematic view of the integral self-contained drillstring compensator showing the operation of extending a cylinder rod of the integral self-contained drillstring compensator in accordance with an exemplary embodiment;

FIG. 5 is a cross-sectional schematic view of the integral self-contained drillstring compensator showing the operation of retracting the cylinder rod of the integral self-contained drillstring compensator in accordance with an exemplary embodiment;

FIG. 6 is a schematic view of the hydraulic and pneumatic layout of the integral self-contained drillstring compensator in accordance with an exemplary embodiment; and

FIG. 7 is a graphical view of a pressure-hook load graph showing the relationship between a hook load and a nominal required system pressure for the integral self-contained drillstring compensator in accordance with an exemplary embodiment.

The drawings illustrate only exemplary embodiments of the invention and are therefore not to be considered limiting of its scope, as the invention may admit to other equally effective embodiments. The elements and features shown in the drawings are not necessarily to scale, emphasis instead being placed upon clearly illustrating the principles of the exemplary embodiments. Additionally, certain dimensions or positionings may be exaggerated to help visually convey such principles.

DETAILED DESCRIPTION OF THE EXEMPLARY EMBODIMENTS

The exemplary embodiments disclosed herein are directed to systems, methods, and devices for providing an integral self-contained drillstring compensator that includes a cylinder assembly, an accumulator, and at least one air pressure cylinder and will be described more fully hereinafter with reference to the accompanying drawings, in which exemplary embodiments are shown. This invention may, however, be embodied in many different forms and should not be construed as limited to the embodiments set forth herein; rather, these embodiments are provided so that this disclosure will be thorough and complete, and will fully convey the scope of the invention to those skilled in the art. The invention is better understood by reading the following description of non-limiting, exemplary embodiments with reference to the attached drawings, wherein like parts of each of the figures are identified by like reference characters, and which are briefly described as follows.

FIG. 1 is a partial schematic representation of a derrick 110 and a drill floor 120 of a floating vessel 100 showing an integral self-contained drillstring compensator 150 and the various positions of the integral self-contained drillstring compensator 150 during installation in accordance with an exemplary embodiment. The integral self-contained drillstring compensator 150 includes at least one high pressure air cylinder 210 (FIG. 2), an accumulator 240 (FIG. 2), and a compensating cylinder 260 (FIG. 2), which are fluidly coupled to one another, as will be described in more detail with respect to FIGS. 2-5.

The floating vessel 100 includes the drill floor 120, the derrick 110, and the catwalk 130. The drill floor 120 is disposed substantially in a horizontal direction that is above and substantially parallel to the surface of the water level (not shown). The drill floor 120 is the area on the floating vessel 100 where the tools are located to make the connections of the drill pipe, bottom hole assembly, tools and bit. The drill floor 120 is considered the main area where work is performed.

The derrick 110 extends vertically upward from the drill floor 120. The derrick 110 is the support structure for the equipment used to lower and raise the drill string and/or other equipment into and out of the wellbore (not shown). The derrick 110 includes a crown block 112, a travelling block 114, a top drive 116, and an elevator 118. The crown block 112 is positioned at the top of the derrick 110 and is the stationary section of a block and tackle that contains a set of pulleys or sheaves through which the drill line (wire rope) is threaded or reeved and is opposite and above the traveling block 114. The traveling block 114 is the freely moving section of the block and tackle and is opposite and under the crown block 112. The combination of the traveling block 114, the crown block 112 and wire rope drill line gives the ability to lift weights in the hundreds of thousands of pounds. The crown block 112 is coupled to the travelling block 114 via wires or cables. The top drive 116 is a mechanical device on a floating vessel 100 that provides clockwise torque to the drill string to facilitate the process of drilling a borehole or to provide torque on other equipment to facilitate in the production of oil and gas. The top drive 116 is an alternative to rotary table and is located at the swivel place and allows a vertical movement up and down the derrick 110. The top drive 116 is coupled adjacent to the travelling block 114. The top drive 116 is coupled to the elevator 118 via a plurality of bails (not shown). The elevator 118 is a hinged device that is used to latch to the drill pipe or casing to facilitate the lowering or lifting (of pipe or casing) into or out of the wellbore. The elevator 118 may also be used to latch to other equipment to be place along the drillstring line or production line.

The catwalk 130 is located adjacent the drill floor 120 and includes a riser skate 135 for rolling drill pipe, casing, production tubing and tools onto the drill floor 120. The travelling block 114 travels downward to allow the elevator 118 to couple with the drill pipe, casing, production tubing, tool, or other piece of equipment and raise it into the derrick 110 by retracting upwards.

According to FIG. 1, the integral self-contained drillstring compensator 150 is placed horizontally on the riser skate 135 of the catwalk 130. According to certain exemplary embodiments, while the integral self-contained drillstring compensator 150 is on the riser skate 135, the accumulator 240 (FIG. 2) of the integral self-contained drillstring compensator 150 is filled with a fluid 430 (FIG. 4), which will be described in more detail with respect to FIG. 4. The volume of fluid 430 (FIG. 4) used to fill the accumulator 240 (FIG. 2) is equal to the volume of the compensating cylinder 260 (FIG. 2). According to certain exemplary embodiments, also while the integral self-contained drillstring compensator 150 is on the riser skate 135, the high pressure air cylinder 210 (FIG. 2) of the integral self-contained drillstring compensator 150 is filled with a compressible gas 420 (FIG. 4), which will be described in more detail with respect to FIG. 4. The volume of compressible gas 420 (FIG. 4) used to fill the one or more high pressure air cylinders 210 (FIG. 2) is equal to or greater than the volume of the fluid 430 (FIG. 4) used to fill the accumulator 240 (FIG. 2). According to the present exemplary embodiments, two high pressure air cylinders 210 (FIG. 2) are used; however, according to other exemplary embodiments, a fewer or greater number of high pressure air cylinders 210 (FIG. 2) may be used. Although the fluid 430 (FIG. 4) is used to fill the accumulator 240 (FIG. 2) and the compressible gas 420 (FIG. 4) is used to fill the one or more high pressure air cylinders 210 (FIG. 2) while the integral self-contained drillstring compensator 150 is on the riser skate 135, the filling of the fluid 430 (FIG. 4) and the compressible gas 420 (FIG. 4) may be performed at anytime prior to the integral self-contained drillstring compensator 150 being lifted up into the derrick 110 area.

While on the riser skate 135, the integral self-contained drillstring compensator 150 is rolled along the riser skate 135 to the edge of the riser skate 135 near the drill floor 120. The travelling block 114 is moved axially downward away from the crown block 112 toward the drill floor 120. Once the elevator 118 is adjacent the integral self-contained drillstring compensator 150, the elevator 118 is coupled to a lift sub 152 of the integral self-contained drillstring compensator 150. The lift sub 152 is located at one end of the integral self-contained drillstring compensator 150. It is at this time or prior to this time that the fluid 430 (FIG. 4) and the compressible gas 420 (FIG. 4) are filled into the accumulator 240 (FIG. 2) and the at least one high pressure air cylinders 210 (FIG. 2), respectively. The travelling block 114 is then moved upward, causing the top drive 116, the elevator 118, and the now coupled integral self-contained drillstring compensator 150 to also be moved upward within the derrick 110.

As previously mentioned, the integral self-contained drillstring compensator 150 includes the compensating cylinder 260 (FIG. 2). The compensating cylinder 260 (FIG. 2) includes a cylinder rod 154 which extends out from the compensating cylinder 260 (FIG. 2) or retracts into the compensating cylinder 260 (FIG. 2). As seen in FIG. 1, the cylinder rod 154 is extended twenty feet from the compensating cylinder 260 (FIG. 2) towards the drill floor 120. Although the cylinder rod 154 extends twenty feet away from the compensating cylinder 260 (FIG. 2), the cylinder rod 154 may be designed to extend a lesser distance or a greater distance from the compensating cylinder 260 (FIG. 2) in other exemplary embodiments. According to some exemplary embodiments where the cylinder rod 154 is capable of extending twenty feet away from the compensating cylinder 260 (FIG. 2), the cylinder rod 154 is designed to extend to its median point, which is ten feet away from the compensating cylinder 260 (FIG. 2), such that the cylinder rod 154 compensates the remaining distance in each direction, which is ten feet in either direction according to this exemplary embodiment, during operation.

At the end of the cylinder rod 154, which is away from the compensating cylinder 260 (FIG. 2), is a lower sub 156. The lower sub 156 is located at an opposite end of the integral self-contained drillstring compensator 150 than the lift sub 152. The low sub 156 is used to couple with other drill pipes, casings, production tubings and/or tools. Hence the integral self-contained drillstring compensator 150 is installed in an in-line position with drill pipes, casings, production tubings and/or tools used in drilling a well, production of the well, testing of the well, or intervention of the well.

FIG. 2 is a partial perspective view of the integral self-contained drillstring compensator 150 of FIG. 1 in accordance with an exemplary embodiment. FIGS. 3A-3D are several views of the integral self-contained drillstring compensator 150 of FIG. 2 in accordance with an exemplary embodiment. Specifically, FIG. 3A is a side view of the integral self-contained drillstring compensator 150 in accordance with an exemplary embodiment; FIG. 3B is a rotated side view of the integral self-contained drillstring compensator 150 in accordance with an exemplary embodiment; FIG. 3C is a front view of the integral self-contained drillstring compensator 150 in accordance with an exemplary embodiment; and FIG. 3D is a rear view of the integral self-contained drillstring compensator 150 in accordance with an exemplary embodiment. Referring to FIGS. 1-3D, the integral self-contained drillstring compensator 150 includes the at least one high pressure air cylinder 210, the accumulator 240, and the compensating cylinder 260 (FIG. 2), which are fluidly coupled to one another, according to some exemplary embodiments. According to some exemplary embodiments, the integral self-contained drillstring compensator 150 also includes an optional low pressure air cylinder 380.

The at least one high pressure air cylinder 210 includes a first high pressure air cylinder 212 and a second high pressure air cylinder 314 according to certain exemplary embodiments; however, there may be additional or fewer high pressure air cylinders in other exemplary embodiments. Each of the high pressure air cylinders 212, 314 is fabricated from AISI860 material and has a capacity of 700 gallons each. However, in other exemplary embodiments, one or more of the high pressure air cylinders 212, 314 may be constructed using a different suitable material or a different capacity based upon the skill and knowledge of a person having ordinary skill in the art and having the benefit of the present disclosure. The capacity of the high pressure air cylinders 212, 314 may be based upon the amount of weight to be lifted, the compensation to be provided, and/or the space requirements of the floating vessel 100. Further, the first and second high pressure air cylinders 212, 314 are designed to operate under a minimum operating pressure of 350 pounds per square inch (psi) and a maximum operating pressure of 3000 psi. As will be described later with respect to FIG. 7, the first and second high pressure air cylinders 212, 314 are charged with a compressible gas 420 (FIG. 4) at about 2800 psi prior to being installed into the derrick 110 portion of the floating vessel 100, so that 500 tons can be compensated.

The first and second high pressure air cylinders 212, 314 are filled with the compressible gas 420 (FIG. 4), such as nitrogen in accordance with an exemplary embodiment; however, according to other exemplary embodiments, air or some other compressible gas or fluid may be used in lieu of or in addition to the nitrogen that is used to fill the first and second high pressure air cylinders 212, 314. Also, each of the high pressure air cylinders 212, 314 has a thirty inch diameter bore that provides for an air channel extending longitudinally therethrough. The first high pressure air cylinder 212 and the second high pressure air cylinder 314 are fluidly coupled to each other using a high pressure air cylinder connector 216. The high pressure air cylinder connector 216 fluidly couples one end of the first high pressure air cylinder 212 to one end of the second high pressure air cylinder 314 at the end positioned closer to the lift sub 152. Although the high pressure air cylinder connector 216 is located at the end positioned closer to the lift sub 152 according to some exemplary embodiments, the high pressure air cylinder connector 216 may be coupling the first high pressure air cylinder 212 and the second high pressure air cylinder 314 in a different manner in other exemplary embodiments. According to the exemplary embodiment, the high pressure air cylinder connector 216 is coupled between the first and second high pressure air cylinders 212, 314 so as to provide the compressible gas 420 (FIG. 4) that therein to the accumulator 240 in series with the first high pressure air cylinder 214 providing a fluid connection, which is described in further detail below, to the accumulator 240. The first and second high pressure air cylinders 212, 314 are both arranged longitudinally and substantially parallel with respect to the accumulator 240 and the compensating cylinder 260.

The accumulator 240 also is fabricated from AISI860 material and has a capacity of 500 gallons. However, in other exemplary embodiments, the accumulator 240 may be constructed using a different suitable material or a different capacity based upon the skill and knowledge of a person having ordinary skill in the art and having the benefit of the present disclosure. The capacity of the accumulator 240 may be based upon the amount of weight to be lifted, the compensation to be provided, and/or the space requirements of the floating vessel 100. Further, the accumulator 240 is designed to operate under a minimum operating pressure of 350 psi and a maximum operating pressure of 3000 psi.

The accumulator 240 is filled with a fluid 430 (FIG. 4), such as HoughtoSafe, which includes ethylene glycol, in accordance with an exemplary embodiment; however, according to other exemplary embodiments, CTF, water, glycol, or some other suitable fluid may be used in lieu of or in addition to the HoughtoSafe fluid that is used to fill the accumulator 240. Also, the accumulator 240 has a twenty-five inch diameter bore that provides for a fluid channel therethrough. The accumulator 240 is fluidly coupled to the first high pressure air cylinder 214 using an air cylinder/accumulator connector 342. The air cylinder/accumulator connector 342 fluidly couples one end of the first high pressure air cylinder 212 to one end of the accumulator 240 at the end closer to the lower sub 156, the end opposite the lift sub 152. Although the air cylinder/accumulator connector 342 is located at the end closer to the lower sub 156 according to some exemplary embodiments, the air cylinder/accumulator connector 342 may be coupling either the high pressure air cylinders 212, 314 and the accumulator 240 in a different manner in other exemplary embodiments. A valve (not shown) is placed along the air cylinder/accumulator connector 342 so that the compressible gas 430 (FIG. 4) may be controlled entering and exiting the accumulator 240 in certain exemplary embodiments. This valve may be throttled during operation. The accumulator 240 is arranged longitudinally and substantially parallel with respect to the first and second high pressure air cylinders 212, 314 and the compensating cylinder 260.

The compensating cylinder 260 also is fabricated from AISI860 material and includes the cylinder rod 154 therein. However, in other exemplary embodiments, the compensating cylinder 260 may be constructed using a different suitable material based upon the skill and knowledge of a person having ordinary skill in the art and having the benefit of the present disclosure. The compensating cylinder 260 is designed to operate under a minimum operating pressure of 350 psi and a maximum operating pressure of 3000 psi.

The compensating cylinder 260 has a twenty-three inch bore according to some exemplary embodiments; however, the size of the bore may be different according to other exemplary embodiments. The cylinder rod 154 is 8.4 inches in diameter and is fabricated using 17-4 PH H1150 material; however, the cylinder rod 154 may be constructed using a different suitable material based upon the skill and knowledge of a person having ordinary skill in the art and having the benefit of the present disclosure. The cylinder rod 154 has a 240 inch stroke, or 20 feet stroke, and is designed to extend outwardly from the compensating cylinder 240 by its entire stroke length. As previously mentioned, although the stroke length is twenty feet, the cylinder rod 154 is positioned normally extended to ten feet, such that there is ten feet of compensation available in both directions during operation. The compensating cylinder 260 includes the lift sub 152 at one end and is positioned closer to the crown block 112 during installation and operation on the floating vessel 100. The compensating cylinder 260 also includes the lower sub 156 at its opposing end opposite the end where the lift sub 152 is positioned. This lower sub 156 is used to couple with other pipes, casings, tubings, and other equipment that may be used during testing, intervention, drilling, or production.

The compensating cylinder 260 is fluidly coupled to the accumulator 240 using an accumulator/compensating cylinder connector 262. The accumulator/compensating cylinder connector 262 fluidly couples one end of the accumulator to one end or adjacent to one end of the compensating cylinder 260 at the end closer to the lift sub 152. Although the accumulator/compensating cylinder connector 262 is located at or near the end closer to the lift sub 152 according to some exemplary embodiments, the accumulator/compensating cylinder connector 262 may be coupling the accumulator 240 and the compensating cylinder 260 in a different manner in other exemplary embodiments.

A control valve 264 is placed along the air accumulator/compensating cylinder connector 262 so that the fluid 430 (FIG. 4) may be controlled entering and exiting the compensating cylinder 260 from the accumulator 240 in both directions in certain exemplary embodiments. This control valve 264 may be throttled during operation and may be controlled remotely using a hand device (not shown), a computer (not shown), some instrument panel (not shown), or by some other known devices or methods. According to certain exemplary embodiments, the control valve 264 is an Olmsted flow shut-off valve. In the open position, fluid 430 (FIG. 4) passes freely back and forth from the accumulator 240 to the compensating cylinder 260 and the flow shut-off feature is enabled. The purpose of the flow shut-off feature is to guard against failure of the casing or conductor for which the integral self-contained drillstring compensator 150 is providing tension. In the event of such sudden failure, there will be a rapid retraction of the cylinder rod 154 and a rush of flow from the accumulator 240 to the compensating cylinder 260. When this flow exceeds the maximum design flow setting, which is based upon the normal heave period and amplitude of the heave, of the Olmsted valve 264, the valve 264 will rapidly close to prevent the cylinder rod 154 from slamming into its fully retracted position. The normal range of motion within the integral self-contained drillstring compensator 150 will leave sufficient clearance for this rapid acceleration and cylinder rod 154 retraction and shut-off to occur without slamming into the end stops. Once the control valve 264 is triggered closed, a small amount of fluid 430 is allowed to pass through the control valve 264, allowing a controlled reaction of the compensating cylinder 260 until the cylinder rod 154 is fully retracted. The compensating cylinder 260 is arranged longitudinally and substantially parallel with respect to the first and second high pressure air cylinders 212, 314 and the accumulator 240.

According to an exemplary embodiment, the components of the integral self-contained drillstring compensator 150 are arranged into a triangular-shaped cross-section. The first high pressure air cylinder 212, the second high pressure air cylinder 314, and the accumulator 240 are positioned at the apexes of an isosceles triangle. The maximum distance between the outer walls of the high pressure air cylinders 212, 314 is about 108 inches, while the maximum distance between the outer wall of the accumulator 240 and outer walls of each of the first and second high pressure air cylinders 212, 314 is about 115 inches. The compensating cylinder 260 is positioned substantially in the center of the triangular cross-section with each of the accumulator 240 and the first and second high pressure air cylinders 212, 314 being coupled to the compensating cylinder 260 with one or more coupling brackets 290.

According to some exemplary embodiments, as previously mentioned, the integral self-contained drillstring compensator 150 includes the optional low pressure air cylinder 380. The low pressure air cylinder 380 also is fabricated from AISI860 material and has a capacity of 100 gallons. However, in other exemplary embodiments, the low pressure air cylinder 380 may be constructed using a different suitable material or a different capacity based upon the skill and knowledge of a person having ordinary skill in the art and having the benefit of the present disclosure. The capacity of the low pressure air cylinder 380 may be based upon the amount of weight to be lifted, the compensation to be provided, and/or the space requirements of the floating vessel 100. Further, the low pressure air cylinder 380 is charged with a low pressure compressible gas 440 (FIG. 4) to approximately 35 psi prior to being installed into the derrick 110 portion of the floating vessel 100.

The low pressure air cylinder 380 is filled with a low pressure compressible gas 440 (FIG. 4), such as nitrogen in accordance with an exemplary embodiment; however, according to other exemplary embodiments, air or some other suitable compressible fluid may be used in lieu of or in addition to the nitrogen gas that is used to fill the low pressure air cylinder 380. Also, the low pressure air cylinder 380 has a fifteen inch diameter bore that provides for a gas channel therethrough. The low pressure air cylinder 380 is fluidly coupled to the compensating cylinder 260 using an low pressure air cylinder/compensating cylinder connector 384. The low pressure air cylinder/compensating cylinder connector 384 fluidly couples one end of the low pressure air cylinder 380, the end closer to the lower sub 156, to one end of the compensating cylinder 260, also the end closer to the lower sub 156. Although the low pressure air cylinder/compensating cylinder connector 384 is located at the end closer to the lower sub 156 according to some exemplary embodiments, the low pressure air cylinder/compensating cylinder connector 384 may be coupling the low pressure air cylinder 380 and the compensating cylinder 260 in a different manner in other exemplary embodiments. The low pressure air cylinder 380 is arranged longitudinally and substantially parallel with respect to the first and second high pressure air cylinders 212, 314, the accumulator 240, and the compensating cylinder 260. According to some exemplary embodiments, the low pressure air cylinder 380 is positioned adjacent an outer wall of the compensating cylinder 260 between the accumulator 240 and the first high pressure air cylinder 212. According to some exemplary embodiments, the low pressure air cylinder 380 is coupled to the compensating cylinder 260 with one or more coupling brackets 290. Although the low pressure air cylinder 380 is shown to be positioned in a certain manner according to FIGS. 3A-3D, the low pressure air cylinder 380 may be positioned in a different manner with the low pressure air cylinder/compensating cylinder connector 384 also being routed in a different manner. According to some exemplary embodiments where the low pressure air cylinder 380 is not included in the integral self-contained drillstring compensator 150, the low pressure air cylinder/compensating cylinder connector 384 is routed from the compensating cylinder 380 to the atmosphere. Hence, when the integral self-contained drillstring compensator 150 includes the low pressure air cylinder 380, the integral self-contained drillstring compensator 150 is a closed-system; while when the integral self-contained drillstring compensator 150 does not include the low pressure air cylinder 380, the integral self-contained drillstring compensator 150 is an open-system.

FIG. 4 is a cross-sectional schematic view 400 of the integral self-contained drillstring compensator 150 showing the operation of extending the cylinder rod 154 of the integral self-contained drillstring compensator 150 in accordance with an exemplary embodiment. FIG. 5 is a cross-sectional schematic view 500 of the integral self-contained drillstring compensator 150 showing the operation of retracting the cylinder rod 154 of the integral self-contained drillstring compensator 150 in accordance with an exemplary embodiment. FIG. 6 is a schematic view of the hydraulic and pneumatic layout 600 of the integral self-contained drillstring compensator 150 in accordance with an exemplary embodiment. Referring to FIGS. 4-6, the operation of extending and retracting the cylinder rod 154 of the integral self-contained drillstring compensator 150 is explained. Further FIGS. 4-6 are schematic views for understanding the operation of the integral self-contained drillstring compensator 150 and may not include all details of the components or the piping layouts.

Compressed gas 420 is filled into the high pressure air cylinders 212, 314 as previously mentioned. Also, fluid 430 is filled into the accumulator 240 as previously mentioned. When causing the cylinder rod 154 to retract into the integral self-contained drillstring compensator 150 as seen in FIG. 5, at least a portion of the compressed gas 420 exits the first and second high pressure air cylinders 212, 314 into the air cylinder/accumulator connector 342 and into one end of the accumulator 240 near the lower sub 156. The compressed gas 420 fills into the accumulator 240 and pushes an accumulator cap 425 away from the one end of the accumulator 240 near the lower sub 156 and towards the opposing end of the accumulator 240 near the riser sub 152. The accumulator cap 425 is axially movable along the bore of the accumulator 240 and is used to separate the compressed gas 420 from the fluid 430. The accumulator cap is sized to the diameter of the bore of the accumulator 240. The compressed gas 420 applies a force onto the accumulator cap 425 causing it to move and apply a force onto the fluid 430. As the accumulator cap 420 moves towards the opposing end of the accumulator 240 near the riser sub 152, the accumulator cap 425 applies a force onto the fluid 430 causing at least a portion of the fluid 430 to exit the accumulator 240 and enter the compensating cylinder 260 through the accumulator/compensating cylinder connector 262. As previously mentioned, the accumulator/compensating cylinder connector 262 has a control valve 264 that is used to regulate the amount of fluid 430 that travels between the accumulator 240 and the compensating cylinder 260 in both directions. The fluid 430 enters the compensating cylinder 260 near the end of the lower sub 156. The fluid 430 fills the portion of the bore of the compensating cylinder 260 around the cylinder rod 154. As the fluid 430 fills that portion of the bore of the compensating cylinder 260, the fluid 430 exerts a force onto a cylinder cap 435 causing the cylinder cap 435 to move axially away from the end of the compensating cylinder 260 near the lower sub 156 towards the opposite end of the compensating cylinder 260 near the riser sub 152. As the cylinder cap 435 moves in that direction, the cylinder rod 154 also retracts into the bore of the compensating cylinder 260 because the cylinder rod 154 is coupled to the cylinder cap 435. Also, as the cylinder cap 435 moves in that direction, it applies a force onto the low pressure compressible gas 440 causing at least apportion of the low pressure compressible gas 440 to exit the compensating cylinder 260 through the low pressure air cylinder/compensating cylinder connector 384. In the exemplary embodiments where there is a low pressure air cylinder 380, the low pressure compressible gas 440 enters the low pressure air cylinder 380. However, in the exemplary embodiments where there is no low pressure air cylinder 380, the low pressure compressible gas 440 exits the compensating cylinder 260 into the atmosphere. This retraction of the cylinder rod 154 occurs during operation when the floating vessel 100 descends to a trough of a wave, or pulse.

When causing the cylinder rod 154 to extend out of the integral self-contained drillstring compensator 150 as seen in FIG. 4, such as when the floating vessel 100 is at the crest, or top, of the wave, or pulse, the cylinder cap 435 along with the cylinder rod 154 moves further away from the lift sub 152. As the cylinder cap 435 along with the cylinder rod 154 moves further away from the lift sub 152, at least a portion of the low pressure compressible gas 440 from the low pressure air cylinder 380 exits the low pressure air cylinder 380 and enters the compensating cylinder 260 through the low pressure air cylinder/compensating cylinder connector 384. In the exemplary embodiments that do not include the low pressure air cylinder 380, the low pressure compressible gas 440 enters the compensating cylinder 260 from the atmosphere. This low pressure compressible gas 440 fills the portion of the bore of the compensating cylinder 260 that is between the cylinder cap 435 and the end of the compensating cylinder 260 that is closer to the lift sub 152. As the cylinder cap 435 along with the cylinder rod 154 moves further away from the lift sub 152, the cylinder cap 435 exerts a pressure on the fluid 430 that is in the bore of the compensating cylinder 260 between the cylinder cap 435 and the end of the compensating cylinder 260 that is closer to the lower sub 156. The fluid 430 exits the compensating cylinder 260 and enters the accumulator 240 through the accumulator/compensating cylinder connector 262, which also has the control valve 264 along its path. The control valve 264 controls the amount of fluid 430 that travels from the compensating cylinder 260 to the accumulator 240. As the fluid 430 enters the bore of the accumulator 240 near the end closer to the lift sub 152, the fluid 430 exerts a force onto the accumulator cap 425 causing the accumulator cap 425 to move in an axial direction within the bore of the accumulator 240 in a direction away from the lift sub 152 and toward the lower sub 156. As the accumulator cap 425 moves in that direction, the accumulator cap 425 exerts a force onto the compressible gas 420 within the accumulator 240, thereby causing at least a portion of the compressible gas 420 to exit the accumulator and enter the first high pressure air cylinder 212 through the air cylinder/accumulator connector 342. As the compressed gas 420 enters the first high pressure air cylinder 212, at least a portion of the compressed air 420 in the first high pressure air cylinder 212 exits the first high pressure air cylinder 212 and enters the second high pressure air cylinder 314 through the high pressure air cylinder connector 216. This extending of the cylinder rod 154 occurs during operation when the floating vessel 100 ascends to a crest of a wave, or pulse. As previously mentioned, the pipe routing may be altered in other exemplary embodiments. Further, although the movement of compressible gas 420, fluid 430, and low pressure compressible gas 440 is described in a manner with respect to FIG. 4 so as to extend the cylinder rod 154 and is described in a manner with respect to FIG. 5 so as to retract the cylinder rod 154, the entrances and exits of compressible gas 420, fluid 430, and low pressure compressible gas 440 into and out of the components of the integral self-contained drillstring compensator 150 may be altered such that when the compressed air 420 exits the high pressure air cylinders 212, 314 and flows into the accumulator 240, the cylinder rod 154 is extended instead of retracted; and when the compressed air 420 flows into the high pressure air cylinders 212, 314 from the accumulator 240, the cylinder rod 154 is retracted instead of extended according to other exemplary embodiments. Those people having ordinary skill in the art would be able to achieve this in light of the present disclosure provided herein.

Hence, as described above, as the cylinder rod 154 of the compensating cylinder 260 strokes in (retracts) and out (extends), the compressible gas 410 that resides within the high pressure air cylinders 212, 314 compresses and decompresses. It is the pressure from this compressible gas 410 that creates tension that the integral self-contained drillstring compensator 150 then exerts on the drillstring or landing string.

FIG. 7 is a graphical view of a pressure-hook load graph 700 showing the relationship between a hook load 715 and a nominal required system pressure 735 for the integral self-contained drillstring compensator 150 (FIG. 1) in accordance with an exemplary embodiment. Referring to FIG. 7, the pressure-hook load graph 700 includes the hook load 715 along an x-axis 710 and the nominal required system pressure 735 along a y-axis 730. The relationship between the hook load 715 and the nominal required system pressure 735 is a direct relationship, in that as the hook load 715 increases, the nominal required system pressure 735 also increases.

The integral self-contained drillstring compensator 150 (FIG. 1) is designed to have a capacity of 750 tons when the cylinder rod 154 (FIG. 1) is in a locked position and a capacity of 500 tons when the cylinder rod 154 (FIG. 1) is in an unlocked position, or a position where it provides compensation. According to the pressure-hook load graph 700, the nominal required system pressure 735 that is needed when the hook load 715 is 500 tons (when providing compensation) is about 2800 psi. Five hundred tons is the same as 1000 kilopounds (“kips”). Thus, the nominal required system pressure 735 in the high pressure air cylinders 212, 314 (FIGS. 2 and 3, respectively) should be 2800 psi so that the hook load 715 of the integral self-contained drillstring compensator 150 (FIG. 1) is the designed 500 tons, or 1000 kips. This nominal required system pressure 735 of 2800 psi allows the up and down compensation from the midpoint (i.e., ten feet) on twenty feet of the cylinder rod 154 (FIG. 1). The pressure-hook load graph 700 shows the different nominal required system pressures 735 for different hook loads 715 that may be used in other operating parameters, as needed.

Referring to FIGS. 1-7, according to certain exemplary embodiments, the integral self-contained drillstring compensator 150 is designed to be used as a tension compensator during times when the drill pipe or casing is latched to the well. The passive-in-line integral self-contained drillstring compensator 150 is to be used to mitigate the risk of accidental lockup of the primary heave compensation system. In the event of a primary system lockup, the in-line passive integral self-contained drillstring compensator 150 automatically activates and takes over the compensation duties. The integral self-contained drillstring compensator 150 is to be utilized in series with the main compensator so that it will be active should the primary means of compensation fail. The integral self-contained drillstring compensator 150 is installed vertically in the derrick 110 portion of the floating vessel 100 and receives energy from a self-contained high pressure/liquid system as described in detail above.

According to some exemplary embodiments, the integral self-contained drillstring compensator 150 is designed to have a 750 ton locked capacity and a 500 ton compensating capacity. The total stroke of the cylinder rod 154 is twenty feet, but is design to be at the ten feet midpoint, thereby allowing up to ten feet of compensation in either direction. The dry weight of the integral self-contained drillstring compensator 150 is about 128,000 pounds. The test pressure is 4500 psi, while the maximum operating pressure is 3000 psi and the minimum operating pressure is 350 psi. The service temperature is designed to be a maximum of 120° F. and a minimum of −4° F. As previously mentioned, the fluid 430 is HoughtoSafe or equivalent and the compressible gas 410, 430 is dry nitrogen. Although these are the design parameters of the integral self-contained drillstring compensator 150 according to some exemplary embodiments, other exemplary embodiments may have different design parameters and would not depart from the scope and spirit of the present disclosure.

Although the inventions are described with reference to exemplary embodiments, it should be appreciated by those skilled in the art that various modifications are well within the scope of the invention. From the foregoing, it will be appreciated that an embodiment of the present invention overcomes the limitations of the prior art. Those skilled in the art will appreciate that the present invention is not limited to any specifically discussed application and that the exemplary embodiments described herein are illustrative and not restrictive. From the description of the exemplary embodiments, equivalents of the elements shown therein will suggest themselves to those skilled in the art, and ways of constructing other embodiments of the present invention will suggest themselves to practitioners of the art. Therefore, the scope of the present invention is not limited herein. 

We claim:
 1. A method of installing an integral self-contained drillstring compensator on a floating vessel, comprising: placing an integral self-contained drillstring compensator adjacent a drill floor on a floating vessel; charging a first portion of the integral self-contained drillstring compensator with a compressible gas; and lifting the integral self-contained drillstring compensator, after charging the integral self-contained drillstring compensator, into a derrick, the derrick extending substantially vertically upward from the drill floor.
 2. The method of claim 1, further comprising charging a second portion of the integral self-contained drillstring compensator with a fluid prior to lifting the integral self-contained drillstring compensator.
 3. The method of claim 2, wherein the integral self-contained drillstring compensator comprises: at least one high pressure air cylinder; an accumulator fluidly coupled to the at least one high pressure air cylinder; and a compensating cylinder comprising a cylinder rod therein, the cylinder rod being capable of extending outwardly from the compensating cylinder and retracting inwardly into the compensating cylinder, the compensating cylinder being fluidly coupled to the accumulator, wherein the first portion comprises the at least one high pressure air cylinder, and the second portion comprises the accumulator.
 4. The method of claim 3, further comprising charging a third portion of the integral self-contained drillstring compensator with a low pressure compressible gas prior to lifting the integral self-contained drillstring compensator.
 5. The method of claim 4, wherein the integral self-contained drillstring compensator further comprises: a low pressure air cylinder fluidly coupled to the compensating cylinder, wherein the third portion comprises the low pressure air cylinder.
 6. A method of providing heave compensation using an integral self-contained drillstring compensator installed in a derrick of a floating vessel, comprising: providing an integral self-contained drillstring compensator in a derrick of a floating vessel, the integral self-contained drillstring compensator comprising: at least one high pressure air cylinder comprising compressible gas therein; an accumulator fluidly coupled to the at least one high pressure air cylinder, the accumulator comprising a fluid therein; and a compensating cylinder comprising a cylinder rod therein, the cylinder rod being capable of extending outwardly from the compensating cylinder and retracting inwardly into the compensating cylinder, the compensating cylinder being fluidly coupled to the accumulator, receiving a heave load into the integral self-contained drillstring compensator; allowing the compressible gas to fluidly move between the at least one high pressure air cylinder and the accumulator in response to the heave load; allowing the fluid to fluidly move between the accumulator and the compensating cylinder based upon the direction of movement of the compressible gas; providing compensation in response to the heave load by having the cylinder rod extend further outwardly of the compensating cylinder or retract further inwardly into the compensating cylinder based upon the direction of movement of the fluid between the accumulator and the compensating cylinder.
 7. The method of claim 6, wherein the integral self-contained drillstring compensator further comprises a shut-off control valve positioned along a fluid communication extending between the accumulator and the compensating cylinder, the shut-off control valve regulating the amount of fluid flowing in either direction.
 8. The method of claim 6, wherein the cylinder rod extends further outwardly of the compensating cylinder when at least a portion of the fluid moves from the compensating cylinder to the accumulator causing at least a portion of the compressible gas to move from the accumulator to the at least one high pressure air cylinders, and wherein the cylinder rod retracts further inwardly into the compensating cylinder when the compressible gas moves from the at least one high pressure air cylinders to the accumulator causing at least a portion of the fluid to move from the accumulator to the compensating cylinder.
 9. The method of claim 8, wherein the integral self-contained drillstring compensator further comprises a low pressure air cylinder fluidly coupled to the compensating cylinder, the low pressure air cylinder comprising a low pressure compressible gas, wherein when the cylinder rod extends further outwardly of the compensating cylinder, at least a portion of the low pressure compressible gas moves from the low pressure air cylinder into the compensating cylinder, and wherein when the cylinder rod retracts further inwardly into the compensating cylinder, at least a portion of the low pressure compressible gas moves from the compensating cylinder into the low pressure air cylinder.
 10. The method of claim 9, wherein the compressible gas comprises at least one of nitrogen and air and the low pressure compressible gas comprises at least one of nitrogen and air.
 11. The method of claim 9, wherein the accumulator comprises an accumulator cap positioned therein, the accumulator cap axially movable along the inner portion of the accumulator and separates the compressible gas from the fluid, and wherein the compensating cylinder comprises a cylinder cap positioned therein and from which the cylinder rod extends therefrom, the cylinder cap axially movable along the inner portion of the compensating cylinder and separates the fluid from the low pressure compressible gas.
 12. The method of claim 6, wherein the fluid comprises at least one of ethylene glycol, CTF, and water.
 13. An integral self-contained drillstring compensator, comprising: at least one high pressure air cylinder comprising compressible gas therein; an accumulator fluidly coupled to the at least one high pressure air cylinder, the accumulator comprising a fluid therein; and a compensating cylinder comprising a cylinder rod therein, the cylinder rod being capable of extending outwardly from the compensating cylinder and retracting inwardly into the compensating cylinder, the compensating cylinder being fluidly coupled to the accumulator, wherein the compressible gas moves between the at least one high pressure air cylinder and the accumulator, wherein the fluid moves between the accumulator and the compensating cylinder, and wherein each of the at least one high pressure air cylinder and the accumulator are fastenedly coupled to the compensating cylinder.
 14. The integral self-contained drillstring compensator of claim 13, further comprising a shut-off control valve positioned along a fluid communication extending between the accumulator and the compensating cylinder, the shut-off control valve regulating the amount of fluid flowing in either direction.
 15. The integral self-contained drillstring compensator of claim 13, wherein the cylinder rod extends further outwardly of the compensating cylinder when at least a portion of the fluid moves from the compensating cylinder to the accumulator causing at least a portion of the compressible gas to move from the accumulator to the at least one high pressure air cylinders, and wherein the cylinder rod retracts further inwardly into the compensating cylinder when the compressible gas moves from the at least one high pressure air cylinders to the accumulator causing at least a portion of the fluid to move from the accumulator to the compensating cylinder.
 16. The integral self-contained drillstring compensator of claim 15, further comprising a low pressure air cylinder fluidly coupled to the compensating cylinder, the low pressure air cylinder comprising a low pressure compressible gas, wherein when the cylinder rod extends further outwardly of the compensating cylinder, at least a portion of the low pressure compressible gas moves from the low pressure air cylinder into the compensating cylinder, and wherein when the cylinder rod retracts further inwardly into the compensating cylinder, at least a portion of the low pressure compressible gas moves from the compensating cylinder into the low pressure air cylinder.
 17. The integral self-contained drillstring compensator of claim 16, wherein the compressible gas comprises at least one of nitrogen and air and the low pressure compressible gas comprises at least one of nitrogen and air.
 18. The integral self-contained drillstring compensator of claim 16, wherein the accumulator comprises an accumulator cap positioned therein, the accumulator cap axially movable along the inner portion of the accumulator and separates the compressible gas from the fluid, and wherein the compensating cylinder comprises a cylinder cap positioned therein and from which the cylinder rod extends therefrom, the cylinder cap axially movable along the inner portion of the compensating cylinder and separates the fluid from the low pressure compressible gas.
 19. The integral self-contained drillstring compensator of claim 13, wherein the fluid comprises at least one of ethylene glycol, CTF, and water. 